August was a productive month for us as we returned to the shop and ramped up to speed with fresh motivation from AirVenture at the end of July. The major areas of focus were on assembly and installation of the control surfaces, construction of the control system, and construction of the last few production molds.

General Assembly
With the remaining production molds nearing completion, the majority of our work is now focused on builder assembly tasks and documenting this work for the instructions. One of those builder tasks involves bonding the forward and aft sections of the spinner together. The aft section of the spinner contains a pre-molded lip that acts as the bond site and alignment feature for the forward section. These sections were bonded together and documented for the build instructions.

We also completed and documented a few builder assembly tasks in the fuselage and wing. These tasks included installing angle reinforcements into the fuselage to strengthen areas where the wing attaches to the fuselage, as well as on the aft side of the wing under the top and bottom wing skins. These angle reinforcements will arrive with the kit pre-molded and cured, and the builder will only be required to trim and bond them in place. Installation of the exhaust tunnels just behind the firewall was also completed.   

Elevators
We completed more work on the elevators with the installation of the control torque tubes, bellcranks, and counterbalance weights. The counterbalance weights allow the elevator to balance on its hinge line which helps prevent flutter. The masses of the elevators and corresponding counterbalance weights had been predicted in CAD so it was rewarding to see the mass predictions align with the physical parts.

Ailerons
The ailerons require several small solid carbon components that interface with the hinge pins and counterbalance weights. We machined these parts from a solid block of carbon fiber. Machining carbon fiber can always prove to be challenging as it doesn't machine like metal. There is a fine balance between the debris removal, tool engagement, and the tool path strategies themselves to prevent over heating of the part and to ensure a clean, consistent cut. With these parts cut, we were able to bond them to the aileron skins. Final assembly of the ailerons will take place shortly after final machining of the aileron counterbalance components.

Flaps
The DarkAero 1 uses a split flap design. We molded the flaps over a year ago and finally got the chance to see them installed this past month. The flap installation is a builder task so we documented the process to give builders clear direction. The flap hinges are riveted to the lower trailing edge of the wing which requires some localized reinforcements to support their loads. These reinforcements are bonded in place with an epoxy base assembly adhesive.

Control System
We purchased the tubes and rod ends that will be used to control the ailerons and flaps. For the prototype we went with aluminum tubing to accelerate progress towards first flight. For production we are considering making the control tubes out of carbon to shave additional weight.

Molds and Parts
Work continued on the last remaining plugs and molds for the DarkAero 1. We machined the plugs for the spinner bulkhead and the top and bottom halves of the sump tank. The production molds for these were made directly following their completion. We were able to create the carbon fiber spinner bulkhead from the mold, trim it, and perform an initial fit up with the spinner. The bottom half of the fuel sump was also completed at the end of this month, and we will be finishing the top half in the first week of September. 

3D Printing
You may remember our participation in the Wisconsin Governor’s Business Plan Competition back in the spring. One of the outcomes of the competition was that we were awarded some free prototyping services with Midwest Prototyping in Mount Horeb, WI. We didn’t have time to pursue this prize until this past month since we were focused on preparing for AirVenture through July. We took the time in August to meet with Midwest Prototyping and tour their facilities to get a better understanding of their capability. They have a building full of the most advanced 3D printers on the market (and some that aren’t yet on the market). We already built the majority of the prototype DarkAero 1 using vacuum infused carbon fiber, but after talking with Midwest Prototyping we found a few areas where 3D printing might bring value to the program. We will have more information on our use of 3D printing technology in the coming months.

Ryan’s Projects
August was Ryan's last month of his summer internship with DarkAero. Coming off AirVenture, Ryan was kept busy with a number of key projects that helped us accelerate the progress on the DarkAero 1. Below is a condensed list highlighting several of those projects:

-Infusion testing
-Building carbon angle reinforcements
-Tooling board cutting and assembly for plugs
-Control system tubing prep work
-Bonding carbon angle reinforcements (tapes) into wing trailing edges
-Cutting carbon reinforcements for flap hinges
-Making hinge pins for elevators and ailerons

Ryan is headed back to the University of Minnesota to start his junior year studying aerospace engineering. Ryan was our first intern with DarkAero and he definitely set the bar high. He took on both small and large projects that ranged in difficulty from basic shop clean up to the design and construction of aircraft components. We want to thank Ryan for all his hard work and wish him luck on this coming year in school!

Looking Forward
In September we aim to complete the final small production molds for the aircraft - the wing/horizontal tail/vertical tail tips and nose gear doors. We also look forward to manufacturing the final parts using these molds. Our focus will also include finalizing the assembly and builder instructions for the wing. Additionally, we will likely begin manufacturing the engine mount and nose gear components.